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TRIALS OF A MODIFIED SPECIFICATION FOR COMPACTING DENSE ROADBASE AND BASECOURSE COATED MACADAM

Previous research has led to the formulation of revised specification clauses for the compaction of dense roadbase and basecourse coated macadams which, if implemented fully, should result in improvements in compaction in the critical wheelpath zones of about 3 per cent; this would bring about a worthwhile improvement in pavement performance. The revised specification has been applied in four contracts for the construction and reconstruction of motorways. Improvements in compaction of between 1 and 2 per cent were obtained suggesting that, in practice, the specification was being only partly implemented. Comparison of these results with densities achieved in a laboratory compaction test to establish the practical or refusal limit of compaction shows that there is considerable scope for additional compaction on site. Improved compaction is discussed in terms of the major controllable factors in the compaction operation, i.e. method of rolling, laying temperature and layer thickness. If the benefits of levels of compaction close to refusal are to be realised this will normally require the maintenance of laying temperatures close to the permitted maximum, avoidance of thin layers and more effective compaction plant used according to the amended specification.(a) (TRRL)